1. Field of the Invention
The present invention relates generally to an inflator for an air bag or other safety restraint device and, more specifically, to a compact multi-level output hybrid/all-pyrotechnic inflator which can selectively release gas at different rates and levels and thus enable the air bag or another type of inflatable safety restraint device to be deployed at different output levels in accordance with different sensor inputs.
2. Description of the Related Art
Recently, there has been a demand for controlling the rate and amount of inflation of safety devices such as air bag restraint systems in accordance with variables such as passenger size, position, seat belt usage and the velocity of a vehicle at the time of collision.
In order to provide optimal occupant protection, different levels of output are required from the airbag inflator. For example, in a high-speed collision with a large unbelted person, full rapid inflation of the air bag is required to provide the best restraint. In lower speed crashes with smaller sized occupants or even out-of-position occupants, a lower, slower rate of inflation is required so as not to inadvertently injure the occupant but still provide enough inflation to effect appropriate restraint.
In currently available air bag inflators intended for multi-level or variable output function, the performance is accomplished primarily with inflators which are made up of two individual inflators of the same type that may share one manifold, or by individual propellant chambers in a common pressure vessel sharing one common manifold.
Utilizing two separate inflators of the hybrid type, for example, results in large, heavy and expensive designs since nearly every component is duplicated. For example, there are two distinct pressure vessels, with redundant closures, seals, and in some cases diffusers or manifolds. Additionally, there is the added requirement of securing the two inflators to a common platform, which in turn increases cost, weight, and complexity in manufacturing.
The second approach of having separate propellant chambers encapsulated in one common pressure vessel results in more efficient packaging and reduced cost if the components are shared by the two propellant charges. To achieve different levels of inflation, it has been proposed in U.S. Pat. No. 3,773,353 to Trowbridge et al. to provide two separate charges and to ignite one in the event that a slow inflation is required and to ignite both in the event of a high speed collision, thus achieving the very rapid inflation and deployment of the air bag which is necessary under such circumstances. In this device the charges are arranged within a housing which is filled with a non-toxic gas under pressure. This housing is sealed by a burst plate that is punched out by a piston and rod type of arrangement when a first of the two charges is detonated. This arrangement suffers from the drawback of being relatively complex and therefore, relatively expensive. For example, no less than three burst plate arrangements are necessary. Also, the charges are each isolated from the reservoir and reservoir gas by an inner housing and a respective rupturable closure.
U.S. Pat. No. 3,905,515 to Allemann discloses another multi-stage inflator assembly which utilizes two separate charges and which disposes the charges in a chamber which is used to store a non-noxious gas under pressure. However, this arrangement is even more complex than that in U.S. Pat. No. 3,773,353. In this arrangement a portion of the burst disc forms the head of a slidable shuttle valve member which is projectable into an exhaust passage to partially throttle the outflow of gases following a detonation of one or both of the two charges.
Consequently, there is a need for a cost-effective, lightweight, compact, simple multi-level inflator for air bags and the like. This need is met by the new and improved multi-level inflator of the present invention.
It is an object of the present invention, therefore, to overcome the disadvantages of the prior art and to provide a cost-effective, lightweight, compact and simple multi-level inflator which is reliable in operation.
A further object of the present invention is to provide a multi-level inflator with two gas generators, which permits ignition of the gas generators either separately, simultaneously or in a timed sequence to effect air bag inflation at different rates in accordance with sensor inputs resulting from a crash or the like.
It is a further object of the present invention to provide a multi-level inflator which utilizes a common pressure vessel for a hybrid type gas generator and an all-pyrotechnic type gas generator.
Still another object of the present invention is to provide such a multi-level inflator which is simple in construction and easy to assemble to minimize the cost and size of the assembly.
These and other objects of the present invention are achieved by providing a multi-level inflation device for inflating a vehicle safety restraint such as an air bag comprising a common pressure vessel for a primary hybrid type gas generator and a secondary all-pyrotechnic type gas generator that are isolated from each other. Within the scope of the present invention, either gas generator can be the primary one. The gases from the primary and secondary gas generators are directed to a common manifold for inflation of the air bag. The combination of a hybrid gas generator and an all all-pyrotechnic gas generator in a single multi-level inflator minimizes size and cost. Also, simple assembly methods, such as magnetic forming, swaging, crimping and welding may be used to assemble the multi-level inflator because of its simple construction.